This is in the pothole area of Interstate State Park. We learned a lot about these, and they're really interesting. Potholes are perfectly round and drilled down into the rock. The first geologists couldn't understand how they formed, because the rock is much too hard for the typical erosion processes, and also they are so perfectly shaped. There are some unique factors required in order for them to form like this. First, the rock must be very hard, otherwise it would erode completely away. Interstate State Park sits on top of a large 7 mile thick layer of basalt. It's an igneous rock formed by volcanic flows, harder than granite or even steel. Second, there must be a lot of water flow carrying a significant amount of sediment to act as sandpaper and drills. Here the water came from glacial melt, carrying sand and rock. Third, there must be something to create force and turbulent water flow. In this case, there were some angular areas the water had to flow through, creating very strong eddy currents, containing sand and rocks which drilled these holes out in the basalt. Interstate State Park has the highest concentration of potholes in the world.